1. Field of the Invention
The present invention relates to a slip control system for an automotive vehicle and, more particularly, to a slip control system for an automotive vehicle so adapted as to improve a traction control of an internal combustion engine particularly when the internal combustion engine rotates at a speed higher than a given value.
2. Description of the Related Art
Heretofore, there is commercially available a traction control technology that can control an engine output and braking force to be applied to wheels (reduce the engine output or increase the braking force) by detecting an amount of a slip of a driving wheel and making the detected slip amount a target value, in order to prevent acceleration from reducing by causing the driving wheels to slip due to an excessive amount of driving torque at the time when the vehicle is being accelerated (for example, Japanese Patent Unexamined Publication (kokai) No. 1-197,160). A large number of vehicles are provided with a such traction control system and an anti-skid control system.
For the technology of performing the traction control of the internal combustion engine for suppressing a slip of the vehicle, there are generally used actions to retard a timing of ignition and cutting the supply of fuel to a partial number of cylinders as means for restricting the engine output in order to control a slip of the vehicle.
Japanese Patent Unexamined Publication (kokai) No. 60-104,730 discloses a slip control system for an automotive vehicle which is so arranged as to cut the supply of fuel to an entire number of the cylinders when a number of revolutions of the engine becomes higher than a given reference number during the traction control of the engine.
When the number of revolutions of the engine is not high, no problems may arise even if the timing of ignition would be retarded and the supply of fuel to the partial number of the cylinders would be cut in order to perform the traction control. On the other hand, however, when the timing of ignition is retarded at the time of the high number of revolutions of the engine, combustibility of the fuel in the combustion of the engine becomes so poor that unburned fuel is caused to burn strongly in a catalyst unit disposed in the exhaust system, thereby proceeding in deterioration of the catalyst unit due to overheating. Further, if the supply of fuel to the partial number of the cylinders would be cut at the time of the high number of revolutions of the engine, the concentration of oxygen in exhaust gases becomes so high that the combustion of the fuel is accelerated in the catalyst unit, thereby inducing deterioration of the catalyst unit.